A stent is a radially expandable endoprosthesis which is adapted to be implanted in a body lumen. Stents are typically used in the treatment of atherosclerotic stenosis in blood vessels and the like to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system. They have also been implanted in urinary tracts, bile ducts and other bodily lumen. They may be self-expanding or expanded by an internal radial force, such as when mounted on a balloon.
Delivery and implantation of a stent is accomplished by disposing the stent about a distal portion of the catheter, percutaneously inserting the distal portion of the catheter in a bodily vessel, advancing the catheter in the bodily lumen to a desired location, expanding the stent and removing the catheter from the lumen. In the case of a balloon expandable stent, the stent is mounted about a balloon disposed on the catheter and expanded by inflating the balloon. The balloon may then be deflated and the catheter withdrawn. In the case of a self-expanding stent, the stent may be held in place on the catheter via a retractable sheath. When the stent is in a desired bodily location, the sheath may be withdrawn allowing the stent to self-expand.
In the past, stents have been generally tubular but have been composed of many configurations and have been made of many materials, including metals and plastic. Ordinary metals such as stainless steel have been used as have shape memory metals such as Nitinol and the like. Stents have also been made of bio-absorbable plastic materials. Stents have been formed from wire, tube stock, etc. Stents have also been made from sheets of material which are rolled.
A number of techniques have been suggested for the fabrication of stents from sheets and tubes. One such technique involves laser cutting a pattern into a sheet of material and rolling the sheet into a tube or directly laser cutting the desired pattern into a tube. Other techniques involve cutting a desired pattern into a sheet or a tube via chemical etching or electrical discharge machining.
Laser cutting of stents has been described in a number of publications including U.S. Pat. No. 5,780,807 to Saunders, U.S. Pat. No. 5,922,005 to Richter and U.S. Pat. No. 5,906,759 to Richter. Other references wherein laser cutting of stents is described include: U.S. Pat. Nos. 5,514,154, 5,759,192, 6,131,266 and 6,197,048.
An example of a conventional laser for cutting a stent is a highly focused pulsed Nd:YAG laser which has a pulse duration in the range of approximately 0.1 to 20 milliseconds. This is a long pulse time for cutting and characteristically produces a relatively large melt zone and heat affected zone (HAZ) on the metal. The conventional laser cutting process typically results in the formation of melt dross on the inside edge of the cut tube. This dross must be cleaned off in subsequent processes.
Past laser cutting systems typically mount the tube to be cut from a spindle shaft in a horizontal orientation wherein the laser is mounted perpendicular to the longitudinal axis of the tube in a downward looking configuration. Such a horizontal orientation of the stent tube has many drawbacks.
For example, as the tube is being cut, dross and other debris may accumulate in the tube interior. This requires a stream of water to flush the tube to wash away the debris. The horizontal orientation of the tube additionally exacerbates the problem of ridding debris from the tube as debris must be actively driven out the open end of the tube. This necessitates the flushing stream be applied with significant pressure to ensure that debris does not clog the tube end.
Another more serious drawback is that in some cases, particularly in longer tubes, the tube may tend to bow as a result of gravity. Such bowing may interfere with the precise nature of the stent cutting process, resulting in cutting errors or more significant damage to the tube/stent. In addition, as the tube is rotated during cutting, any bowing of the tube will cause the unsecured end of the tube to oscillate resulting in excess strain being placed on the tube, and potentially leading to improper cutting and/or the formation of cutting imperfections.
In light of the above a need exists to provide a laser cutting/processing system wherein the potential for tube bowing and tube oscillation is minimized or removed completely, and where cutting debris such as melt dross is more easily and consistently removed from the tube during processing.
All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims.